Method of producing hydrophilic articles of water-insoluble polymers

ABSTRACT

Hydrophilic films, fibers and spongy articles of a water-insoluble polymer selected from the group consisting of regenerated cellulose, cellulose ether, cellulose ester and polyalkylene, and capable of forming fibers and films, are produced by distributing in a mass of the polymer up to 50% of pulverulent or granular amorphous particles of an originally water-soluble cellulose ether prepared from natural cellulose and rendered by chemical modification at least partly water-insoluble while remaining water-absorbent. The resulting mixture is then processed by conventional methods into the desired article.

This application is a division of copending application Ser. No.838,339, filed Sept. 30, 1977, in turn a continuation of Ser. No.681,730, filed Apr. 29, 1976, now abandoned, in turn a continuationin-part of Ser. No. 535,972, filed Dec. 23, 1974, now abandoned.

The invention relates to articles for example fibers, films and spongyproducts, of polymers of increased hydrophilic character.

It has been proposed to produce articles of regenerated cellulose byintroducing a material which bonds to the cellulose, and contains anactive component, into the cellulose before the final regeneration ofthe latter, note U.S. Pat. No. 3,905,954. The character of the activecomponent can be such that, if desired, the hydrophilic character of theregenerated cellulose is greater than it would be without modificationwith the active component. The structures obtained in accordance withthis process are modified throughout their entire mass. Accordingly,their physical properties differ from those of the correspondingunmodified structures, in accordance with the intended result of thisprocess. However, it may result in an undesired lowering of tensilestrength, extensibility and flexural strength of resulting structures.More importantly, however, the modifications possible are restricted notonly to the manufacture of structures of cellulose or cellulosederivatives but also in the achievable physical effects, for examplewith regard to the permeability of films manufactured by the process towater and other liquids.

In U.S. Pat. Nos. 3,259,537 and 3,275,580, there is described an articleof a mixture of an organic polymer and cellulose crystallite aggregatesor derivatives. Those crystallite aggregates have an average level-offD. P. value in the range of from about 15 to about 375 anhydroglucoseunits and the specific value will be dependent upon the source material,which in all instances has an actual D. P. greater than its averagelevel-off D. P. and was modified by the controlled acid hydrolysis ofcellulose to reflect a destruction of the original amorphous structureof the cellulosic source material. The derivatives of cellulosecrystallite aggregates possess physical characteristics and propertiessimilar to those of cellulose crystallite aggregates.

The present invention provides articles, which have been renderedhydrophilic, of water-insoluble polymers which can be manufactured frompolymeric material other than regenerated cellulose material and can bemanufactured with a great range of hydrophilic properties. The presentinvention provides an article or shaped structure of a polymer capableof forming fibers and films and being water-insoluble, which contains,distributed within its mass or coated on its surface, particles ofcellulose ethers that are inherently water-soluble but have beenrendered at least partly, preferably more than 50% by weight,water-insoluble by chemical modification, but are still capable ofabsorbing water.

The structures or articles constructed according to the invention may beshaped by any process suitable for the shaping of the base polymer. Apulverulent or granular material of modified cellulose ether may, forexample, be added to the polymer mass before shaping and uniformlydistributed therein. Thus, for example the customary precipitationprocesses are used if filaments, films or sponges of regeneratedcellulose are being manufactured, or the casting process is used iffilms of cellulose acetate are being manufactured, while melt extrusionis used principally if structures of polyethylene or other polyalkylenesor other extrusible polymers are being manufactured. Articles which havethe particles as a surface covering are suitably manufactured bysprinkling the supporting article, composed of the polymer, with theparticles, if the surface being sprinkled is either provided with anadhesive or is in a state in which the surface itself acts as anadhesive. The polymeric base mass of the articles according to theinvention can in principle be composed of any polymer from whichself-supporting films, or fibers or filaments, can be manufactured.Further examples of polymers which may be mentioned are water-insolublealkyl cellulose, such as, for example, aqueous alkalisolublehydroxyethyl cellulose, methyl cellulose or hydroxypropyl cellulose,polyacrylonitrile, polyamides, polyethylene, polypropylene andpolyesters, for example polyethylene terephthalate.

The particles are generally finely pulverulent to granular. Theirparticle size is in the range of 0.01 to 2 mm and depends upon the enduse of the structure. The particles are composed of cellulose ethers,such as for example carboxymethyl cellulose, hydroxyethyl cellulose ormethylhydroxyethyl cellulose, which are modified. Examples of possiblemodifying agents for cross-linking are:dimethylolmethylene-bis-acrylamide; methylene-bis-acrylamide;trichloro-pyrimidine, and tetrachloropyrimidine; cyanuric chloride;epichlorohydrin; dichloroacetic acid, diepoxides or their precursorsdi-α-halogenohydrins. Such materials are disclosed in U.S. Pat. Nos.3,589,364, and 3,936,441.

Further examples of possible modifiers are: N-methylolacrylamide;N-(acrylamidomethylene)-acetamide; N-(acrylamidomethylene)-formamide;N-(acrylamidomethylene)-amylurethane;N-(acrylamidomethylene)-methylurethane;N-(acrylamidocarboxymethylene)-ethylurethane;N-(acrylamidomethylene)-methoxyethylurethane and vinyl sulfonamide. Suchmodified cellulose ethers are described in U.S. Pat. No. 3,965,091. Theamount of added modified cellulose ether particles can be varied withinwide limits depending upon what degree or what type of hydrophiliccharacter, for example of swelling capacity or ion exchange capacity, isdesired. However, in general, the maximum amount of additive should belimited such that the mechanical strength of the film or other structureis not significantly reduced. For example, for sodium carboxymethylcellulose (Na-CMC) which is slightly modified and therefore swells verygreatly in water, this maximum is at 50% by weight of the total in abase of regenerated cellulose. In the case of hydroxyethyl cellulose(HEC) of low substitution and cellulose acetate a maximum is reached atabout 30 to 40% by weight of the total. The lower concentration limitdepends upon the nature and on the action which the particles ofmodified cellulose ethers are to bring about.

A parameter which also can be varied within wide limits is the degree ofmodification, for instance of cross-linking of the cellulose ether ofwhich the particles are composed. When using minor amounts of, forinstance, cross-linking agents, for example from 3 to 10% by weight ofepichlorohydrin, relative to Na-CMC, when producing Na-CMC fibers,highly swellable fibers are obtained. At higher degrees ofcross-linking, the swellability of the cellulose ether greatly decreasesand its water-insoluble content increases. If, for example, about 33% byweight of these highly swellable Na-CMC fibers (about 20-fold waterabsorption) are incorporated into a regenerated cellulose film, theswelling factor of the film rises from about 150% (pure regeneratedcellulose) to about 350%.

In order to make modified water-insoluble ionic cellulose ethers morereadily accessible for ion exchange processes it is sometimes advisableto locate them on the surface of a structure, for example of a film. Aregenerated cellulose film of which the surface is covered with theparticles is produced, for example, by sprinkling finely groundcross-linked Na-CMC homogeneously through a sieve onto an as yet notregenerated web of viscose and then regenerating the viscose web in theusual manner to form regenerated cellulose. This gives a hydratedcellulose film coated on one side with cross-linked Na-CMC.

The examples which follow further illustrate the invention. Examples 1to 3 relate to the manufacture of regenerated cellulose films which aremodified with particles of Na-CMC modified by cross-linking withepichlorohydrin. Examples 4 and 5 describe the manufacture of films ofcellulose acetate and particles of cross-linked Na-CMC. In Example 6,particles of cross-linked Na-CMC are used with films of HEC of a lowdegree of etherification as the carrier material. This water-insolubleHEC has an average degree of substitution of about 0.2 and gives a clearsolution in 5 to 8% by weight sodium hydroxide solution; the alkalinefilm can be regenerated by adding acid and a clear film is obtainedwhich is rendered cloudy by the heterogeneous cellulose ether additive.Examples 7 to 13 relate to further films of regenerated cellulose(hydrated cellulose) modified with cross-linked cellulose ethers.Examples 14 to 17 relate to the manufacture of films coated on one sidewith cross-linked cellulose ethers.

The hydrophilic structures according to the invention can be used inmany fields of industry. As films, for example, they can be used as ionexchangers or as dialysis membranes or as osmosis membranes. In the formof fibers they serve for the manufacture of textiles of betterabsorbency for water, which, inter alia, also makes the textilespleasanter to the human skin, or for the manufacture of leather-likeproducts.

EXAMPLE 1

1 g of finely fibrous water-insoluble cross-linked Na-CMC, which wascross-linked with epichlorohydrin, contained about 25% by weight ofsoluble constituents and had a water retention capacity of 20 times itsweight and a theoretical exchange capacity of about 3.5milliequivalents/g, was homogeneously incorporated, in a 3 roll mill,into 100 g of spinnable viscose containing about 10% by weight ofcellulose. A layer of 0.2 to 0.4 mm thickness of the modified viscosewas cast on a glass plate and regenerated in the usual manner. Atransparent regenerated cellulose film was obtained, which as a resultof the embedded water-insoluble cross-linked Na-CMC fibers had a totaltheoretical exchange capacity of about 0.32 milliequivalent/g. The waterretention capacity of the film was about 250% by weight. A cellulosehydrate film manufactured under the same conditions has a waterretention capacity of 125% by weight.

EXAMPLE 2

The expierment was carried out as in Example 1 but the amount ofcross-linked Na-CMC incorporated was increased to 5 g (about 33% byweight of Na-CMC, based on the finished film). Cloudy films with atheoretical exchange capacity of about 1.15 milliequivalents/g wereobtained. Their water-retention capacity was about 370% by weight.

EXAMPLE 3

The procedure of the above Example 1 was followed but the amount ofcross-linked Na-CMC was increased to 10 g (50% by weight of Na-CMC,based on the finished film). An opaque film visually resembling a paperfleece was obtained. The individual fibers were held together by theregenerated cellulose binder. The theoretical exchange capacity wasabout 1.7 milliequivalents/g. The water retention capacity was about390% by weight.

Since the cross-linked Na-CMC withdraws water from the viscose, themixture became difficult to homogenize if Example 1 was carried out withmore than 10 g of cross-linked Na-CMC. On the other hand, though wateror sodium hydroxide solution could be added without difficulty to theviscose, there was then a loss in the strength of the resulting film.

EXAMPLE 4

10 g of slightly cross-linked fibrous Na-CMC were stirred homogeneouslyinto a 15% by weight cellulose acetate solution in acetone so as to givea ratio of cellulose acetate to cross-linked cellulose ether of 1:1. A0.5 mm thick layer was cast and the solvent was evaporated off. In theresulting film, the fibers of cross-linked Na-CMC fibers were embeddedin a transparent layer of cellulose acetate so that the film was opaquewhite. The theoretical exchange capacity of the film was about 1.7milliequivalents/g. Its water retention capacity was about 350% byweight. The water retention capacity of a cellulose acetate film, incontrast, is only 20% by weight.

EXAMPLE 5

The procedure followed was as in Example 4, but the amount ofcross-linked Na-CMC was reduced to half and, after casting, the layerprecipitation was carried out with water. An opaque white membrane wasobtained, which had a theoretical exchange capacity of 1.15milliequivalents/g. Its water retention capacity was about 360% byweight.

EXAMPLE 6

The procedure followed was as in Example 2, but HEC of low degree ofetherification, with an average degree of substitution of about 0.2, wasemployed as the polymeric film material. 5 g of cross-linked Na-CMC wereincorporated homogeneously into 100 g of a 10% by weight solution of theHEC in 8% aqueous NaOH and a film was obtained by precipitating the 0.5mm thick web in dilute sulfuric acid. A transparent film having atheoretical exchange capacity of 1.15 milliequivalents/g and a waterretention capacity of about 150% by weight was obtained.

EXAMPLES 7 to 13

Table 1 summarizes the essential data of Examples 1 to 6 and theirresults, and gives those of a further 7 examples (Examples 7 to 13), inwhich films of regenerated cellulose (hydrated cellulose) which weremodified with cross-linked sodium carboxymethyl cellulose and sodiumcarboxymethylhydroxyethyl cellulose (Na-CMHEC), employing variouscross-linking agents, were manufactured as the polymeric carriermaterial.

                                      Table 1                                     __________________________________________________________________________    Cross-linked cellulose ethers, incorporated into cellulose-based films           Polymeric                                                                             Cross-linked                                                                         Cross-     Cross-linked cellulose                                                                    Theoretical ion                                                                            Water retention         Ex.                                                                              carrier cellulose                                                                            linking    ether, % by weight                                                                        capacity, milliequiva-                                                                     capacity of the         No.                                                                              material                                                                              ether  agent      based on film                                                                             lent/g per film                                                                            film, % by              __________________________________________________________________________                                                          weight                  1  Hydrated                                                                              Na-CMC Epichlorohydrin                                                                          10          0.35         250                        cellulose                                                                  2  Hydrated                                                                              Na-CMC Epichlorohydrin                                                                          33          1.15         370                        cellulose                                                                  3  Hydrated                                                                              Na-CMC Epichlorohydrin                                                                          50          1.7          390                        cellulose                                                                  4  Cellulose                                                                             Na-CMC Epichlorohydrin                                                                          50          1.7          350                        acetate                                                                    5  Cellulose                                                                             Na-CMC Epichlorohydrin                                                                          33          1.15         360                        acetate                                                                    6  Hydroxy-                                                                              Na-CMC Epichlorohydrin                                                                          33          1.15         150                        ethyl cellulose                                                            7  Hydrated                                                                              Na-CMC Cyanuric   33          1.15         450                        cellulose      chloride                                                    8  Hydrated                                                                              Na-CMC Dichloroacetic                                                                           33          1.15         308                        cellulose      acid                                                        9  Hydrated                                                                              Na-CMC Dimethylolmethyl-                                                                        33          0.75         240                        cellulose      ene-bis-acrylamide                                          10 Hydrated                                                                              Na-CMC Trichloropyrimidine                                                                      33          0.70         200                        cellulose                                                                  11 Hydrated                                                                              Na-CMC Tetrachloropyrimidine                                                                    33          0.85         240                        cellulose                                                                  12 Hydrated                                                                              Na-CMHEC                                                                             Methylene-bis-                                                                           33          0.51         220                        cellulose      acrylamide                                                  13 Hydrated                                                                              Na-CMC Methylene-bis-                                                                           33          0.94         280                        cellulose      acrylamide                                                  __________________________________________________________________________

EXAMPLE 14

An 0.5 mm thick layer of viscose ripened for spinning (as in the aboveExample 1) was cast onto a glass plate. Thereafter, finely ground dryNa-CMC cross-linked with epichlorohydrin was homogeneously sprinkledover the surface through a sieve of appropriate mesh width. The layerwas regenerated in the usual manner. The film thus obtained was freedfrom loosely adhering Na-CMC by washing with water and plasticized byimmersion in a glycerin-water mixture. A translucent film was obtained,which is composed of regenerated cellulose coated on one side withfragments of water-insoluble cross-linked Na-CMC fibers. The firmlyadhering Na-CMC fibers are freely accessible for ion exchange processes.The theoretical capacity was determined to be about 93.5milliequivalents/square meter or 1.1 milliequivalents/g of film, bymeasuring the difference (in the weight per square meter) compared topure regenerated cellulose. The water retention capacity of the film wasabout 440% by weight.

EXAMPLE 15

A film was cast as in the above Example 4 from a 15% by weight solutionof cellulose acetate in acetone, but before evaporation of the solventcross-linked Na-CMC was homogeneously sprinkled on the film. Atransparent film having a theoretical ion exchange capacity of about 0.9milliequivalents/g and a water retention capacity of about 33% by weightwas obtained.

EXAMPLE 16

An 0.5 mm thick layer was cast as in the above Example 6 from analkaline HEC solution, cross-linked Na-CMC was homogeneously sprinkledon the surface of the layer as in the above Example 14, and a film wasprecipitated and washed. A film having a theoretical exchange capacityof about 1.0 milliequivalent/g of film and a water retention capacity ofabout 130% by weight was obtained.

EXAMPLE 17

The procedure followed was as in the above Example 14 but a Na-CMCcross-linked with cyanuric chloride (instead of with epichlorohydrin)was sprinkled onto the cast viscose layer. The resulting film had atheoretical ion exchange capacity of 1.2 milliequivalents per g of filmand a water retention capacity of 280% by weight.

Table 2 summarizes the essential data of Examples 14 to 17, and theirresults.

                                      Table 2                                     __________________________________________________________________________    Cross-linked cellulose ethers, sprinkled onto the sur-                        face of cellulose-based films                                                                      Theoretical                                                                   ion exchange                                                                  capacity,                                                                            Water reten-                                           Polymeric                                                                          Cross-linked                                                                         Cross-                                                                            milliequi-                                                                           tion capacity                                     Example                                                                            carrier                                                                            cellulose                                                                            linking                                                                           valents per                                                                          of the film,                                      No.  material                                                                           ether  agent                                                                             g of film                                                                            % by weight                                       __________________________________________________________________________    14   Hydrated                                                                           Na-CMC Epi-                                                                              1.1    440                                                    cellulose   chloro-                                                                       hydrin                                                       15   Cellulose                                                                          Na-CMC Epi-                                                                              0.9    33                                                     acetate     chloro-                                                                       hydrin                                                       16   Hydroxy-                                                                           Na-CMC Epi-                                                                              1.0    130                                                    ethyl-      chloro-                                                           cellulose   hydrin                                                       17   Hydrated                                                                           Na-CMC Cyanu-                                                                            1.2    280                                                    cellulose   ric                                                                           chloride                                                     __________________________________________________________________________

EXAMPLE 18

30% by weight of a dry sodium carboxymethyl cellulose cross-linked with50% by weight of epichlorohydrin were homogeneously mixed into finelyground high pressure polyethylene powder. The homogeneous mixture wasgranulated by chopping a strand extruded on a twin screw extruder heaterto 165° C., so that chips, of diameter and height about 3 to 4 mm, ofpolyethylene modified with the cross-linked Na-CMC were produced. Thechips were fibrillated to fibers by means of a cutting mill. The fibroussamples showed a water retention capacity of about 26% and a measurableion exchange capacity of about 0.78 milliequivalent/g.

The starting polyethylene had virtually no water retention capacity, thevalue being 2%.

EXAMPLE 19

To show the difference between modified cellulose ethers made fromnatural cellulose and those made from cellulose crystallite aggregatesin any case, 100 g of cellulose crystallite aggregates in 300 g of 87%isopropanol were alkalized with 46 g of aqueous NaOH solution (50%) bykneading them for 45 minutes at 20° C. Then, the mixture was etherifiedby adding 55 g of sodium monochloracetate and kneading it for anotherhour at 70° C. Then it was cross-linked with 50 g of aqueousdimethylol-methylene-bisacrylamide solution (30%) while it was kneadedfor one hour at 50° C. Then it was neutralized with acetic acid, washedsalt-free with 80% methanol, and dried. The following table 3 shows twoof the physical/chemical properties of the product in each case:

                  Table 3                                                         ______________________________________                                                     Capacity of retaining                                                                         Water-soluble                                                 water, in g of water                                                                          portion, in                                                   per 100 g of modified                                                                         per cent by                                      Source material                                                                            cellulose ether weight                                           ______________________________________                                        natural cellulose                                                                          2895            21                                               cellulose crystal-                                                                         unmeasurably low                                                                              78                                               lite aggregates                                                               ______________________________________                                    

It will be obvious to those skilled in the art that many modificationsmay be made within the scope of the present invention without departingfrom the spirit thereof, and the invention includes all suchmodifications.

What is claimed is:
 1. A process for the production of a hydrophilicfilm, fiber or spongy product of a water-insoluble polymer selected fromthe group consisting of regenerated cellulose, cellulose ether,cellulose ester, and polyalkylene, and capable of forming fibers andfilms, which comprises uniformly distributing in a mass of said polymer,up to 50% by weight of the total weight of said product of pulverulentor granular amorphous particles of an originally water-soluble celluloseether prepared from natural cellulose and rendered by chemicalcross-linking more than 50% by weight water-insoluble while remainingwater absorbent, and shaping the resulting mixture.
 2. A processaccording to claim 1 in which the cellulose ether is cross-linked with across-linking agent selected from the group consisting ofdimethylolmethylene-bis-acrylamide, methylene-bis-acrylamide,trichloro-pyrimidine, tetrachloro-pyrimidine, cyanuric chloride,epichlorohydrin, dichloroacetic acid, diepoxides anddi-α-halogenohydrins.